1. Technical Field
The present invention relates to a monitor, and particularly, to a monitor protection system and a control process of protecting a cathode-ray tube (CRT) monitor from a transient synchronization signal and an abnormal voltage generated from deflection circuits.
2. Related Art
Generally, a display device such as a CRT type of monitor, which is used as either a television monitor or a peripheral device of a computer system, processes information data received from an information data system and provides a visual display of processed information data on a screen. Such a monitor is available in either black and white known as monochrome monitor or high resolution color known as color graphics adapter (CGA), video graphics adapter (VGA) and enhanced graphics adapter (EGA) monitor. Monochrome, CGA, EGA monitors provide a visual display of graphics data by processing digital signals. VGA monitors, by contrast, provide a visual display of graphics data by processing analog signals. In all display devices, the video signal is typically received from a video card installed in an information data system in accordance with vertical and horizontal synchronization signals for a visual display.
Conventional monitor as disclosed, for example, in U.S. Pat. No. 5,072,161 for Deflection Yoke, A Deflection Device And A Monochrome CRT Display issued to Ikeda et al., generally includes a processor which receives the vertical and horizontal synchronization signals to control the visual display of information data on a screen, and vertical and horizontal deflection circuits which respectively receives the vertical and horizontal synchronization signals to perform vertical and horizontal deflection, such that an electron beam generated from an electron gun of a CRT is deflected in a regular sequence from an upper left portion to a lower right portion of the CRT by way of a deflection yoke in order to form an image. Using high voltage technology, a high voltage generating circuit such as disclosed, for example, in U.S. Pat. No. 5,438,245 for High Voltage Generating Circuit issued to Kii et al., is included to stably supply a high voltage to an anode of the CRT for forming an image in response to a flyback pulse generated from the horizontal deflection circuit. A video amplifier then serves to amplify video signals R, G and B transmitted from the video card to approximately 40 Vpp-60 Vpp for providing energy to each picture.
In such a CRT monitor, deflection circuits perform either an electrostatic deflection using an electric field or an electromagnetic deflection using a magnetic field. As a result, an image is formed on the CRT type of monitor from the electron beam projected onto a fluorescent surface thereof and by flowing a toothed waveform of electric current into horizontal and vertical coils using the electromagnetic deflection. However, the deflection circuits are prone to malfunctions, and as a result, excessive voltage is often applied to the CRT monitor causing the monitor to break down. In addition, if excessive synchronization signals are supplied to the CRT monitor, the deflection circuits generate an abnormal deflection signal to the CRT monitor causing the monitor to operate abnormally.
Contemporary techniques for protecting the CRT monitor against excessive voltage are disclosed, for example, U.S. Pat. No. 4,123,166 for High Voltage Protection Circuit issued to Watanabe, U.S. Pat. No. 4,335,335 for Television Receiver High Voltage Protection Circuit issued to Willis, U.S. Pat. No. 4,343,028 for Television Receiver High Voltage Generator Protection Circuit issued to Hicks, U.S. Pat. No. 4,345,275 for High Voltage Protection Circuit For A Television Receiver issued to Waybright, U.S. Pat. No. 4,389,676 for Television Receiver High Voltage Protection Circuit issued to Balaban et al., U.S. Pat. No. 4,459,517 for Horizontal Output Transistor Protection Circuit issued to Hicks, U.S. Pat. No. 4,544,954 for Television Receiver With High Voltage Protection Circuit issued to Chen, U.S. Pat. No. 4,788,618 for High Voltage Protecting Circuit issued to Kimura, U.S. Pat. No. 4,965,496 for Protection Arrangement Of A Deflection Circuit issued to Haferl, U.S. Pat. No. 5,111,122 for Video Display High Voltage Protection Circuit issued to Wilber, U.S. Pat. No. 5,255,147 for Vertical Yoke Protection Circuit issued to Oh, and U.S. Pat. No. 5,430,596 for CRT Protector Circuit issued to Hamaguchi et al. Generally, the excessive voltage which causes abnormal operation of the CRT monitor is detected to ensure normal operation of the deflection circuits.
Recent techniques for protecting operation of a CRT monitor use a micro-processor to detect the abnormal state of horizontal/vertical synchronization signals and a display power management signaling (DPMS) operating system to protect the CRT monitor and the deflection circuits. I have observed, however, that the CRT monitor is still prone to abnormality because the micro-processor cannot reliably determine the normality of deflection signals applied to the CRT monitor. As a result, the CRT monitor may still be damaged due to spot phenomena, etc.